1. Field of the Invention
This invention relates to a photosensitive material for electrophotography, suited for a positive charge system, carried out by a process comprising static charging, exposure and developing.
2. Description of the Prior Art
Photosensitive compounds hitherto used for photosensitive materials for electrophotography include inorganic photoconductive substances and organic photoconductive substances. The former has problems on thermal stability, safety, etc. On the other hand, the latter has excellent safety and economical advantages, and are in recent years prevalent in the photosensitive materials for electrophotography. In the present invention also, the latter organic photoconductive substances are used.
Photosensitive materials or photoconductors for electrophotography (hereinafter often "OPCs") making use of such organic photoconductive substances are usually used in double-layer structure comprised of a charge-generating layer (hereinafter "CG layer") that absorbs light to generate carriers and a charge transport layer (hereinafter "CT layer") that transports the carriers generated, and it is attempted to make them more highly sensitive. In general, in the double-layer structure, the CT layer is formed on the surface side on account of strength, run length, etc., and hence the photosensitive materials are used in a negative charge system.
In such a negative charge system, however, there have been the problems that (1) deterioration due to ozone may occur because of the negative charge used for electrification, (2) the charge may be imperfect and (3) the photosensitive material tends to be affected by the properties of a drum surface.
In order to solve such problems, development is energetically being made on OPCs that employ a positive charge system. In order to accomplish the positive charge system photosensitive material, studies have been made on (1) OPCs of reverse double-layer structure in which the layer structure for the CG layer and CT layer is made reverse to the case of the negative charge system (herein "OPCs-1"), and (2) OPCs of single-layer structure in which a charge-generating agent (herein "CG agent") and a charge-transporting layer (herein "CT agent") are contained together in a single layer (herein "OPCs-2").
In the OPCs-1, however, since the CG layer, which is essentially required to be made thin, is provided on the surface side of the photosensitive material, a decrease in run length and a deterioration of lifetime characteristics are questioned. There are also the problems on the complicated production process and separation of layers that may arise from the double-layer structure. Thus this photosensitive material has not been put into practical use.
The single-layer type OPCs-2 are inferior to the OPCs-1 in respect of sensitivity and charge characteristics (repetition deterioration). In the case of the single-layer type as in OPCs-2, however, there is the advantage that a wear of the photosensitive material does not immediately result in a lowering of run length so long as the agents are uniformly dispersed. In other words, the wear of the photosensitive material is considered to have less influence on its photosensitivity characteristics. The single-layer type OPCs-2 are also advantageous in that they require not so complicated a production process as the double-layer type OPCs-1.